NEW AMINO-ACIDS DERIVED FROM L-PYROGLUTAMIC ACID - SYNTHESIS OF TRANS-4-BENZYL-CIS-5-PHENYL-L-PROLINE, L-ALPHA-(2-BENZYL-3-PHENYLPROPYL)-GLYCINE AND L-ALPHA-(3-PHENYLPROPYL)-GLYCINE

A convenient synthesis of three new amino acids, L-alpha-(3-phenylprop yl)-glycine, L-alpha-(2-benzyl-3-phenylpropyl)-glycine and its conform ationally constrained analog, trans-4-benzyl-cis-5-phenyl-L-proline is reported. All compounds were prepared in good diastereomeric or enant iomeric purity from L-pyroglutamic acid. Trans-4-benzyl-cis-5-phenyl-L -proline was prepared by benzylation of Boc-L-Pyr-OBn, ring opening wi th phenyllithium and subsequent cyclisation. Hydrogenolysis under mild conditions then furnished L-alpha-(2-benzyl-3-phenylpropyl)-glycine. In a similar way, L-alpha-(3-phenylpropyl)-glycine was prepared from c is-5-phenyl-L-proline by catalytic hydrogenolysis. (C) 1998 Elsevier S cience Ltd. All rights reserved.